I am right now up to chapter LII. Answering your question is difficult. I tried to read XLVIII with audio from Vivarium Novum recordings (Livy) and I noticed that there were parts from the recording which were not in the LLPSI text. There is not word change nor adaptation but "suppression" of some parts. Officially *original* Latin begins at XLI.

Actually, real Latin gets incorporated with the adapted right away. Some unadulterated lines of poetry are mixed in with chap 36, and more and larger chunks from the Aeneid in the following chapters on Aeneas. If you don't think those are large enough, spend some time trying to scan the meter and reciting them. In chapter 41, as Gonzalo says, you get a nicely sized chunk from Ovid's Fasti. Take some time and scan and recite that as well.

If you don't find that enough of the original Latin, try what I do. Take a separate composition notebook and use it to record Latin poetry. I use it to put in poetry easy enough for me (see some of the pieces mentioned in their entirety in LL vol 1) like Catullus 3, 5, and some Martial) as well as the selections from the Aeneid in LL vol 2. I them try to scan everything correctly, recite, memorize, etc. It's helpful in that you end up with a little collection of original Latin that you understand thoroughly (as it is introduced to you in LL) that you can go back to and add to as you become familiar with more.

I think there are a few words with more "standard" orthography all the way through the final Cicero and Somnus Scipionis. Earlier in the book Cicero's original "condamnare" is written "condemnare" to reflect the more traditional Latin orthography that came later. Ã˜rberg also does this for his supplements, like Plautus. I don't like it too much â€” an author's orthography is sacredly to be respected, in my opinion (I'm sure someone can challenge me on that however).